Untreated powders tend to stick together due to charges and polarity on the powder surface and minute amounts of impurities, and this interferes with the dispersibility and stability of the powder.
Various types of surface treatment have been proposed to improve the dispersibility and stability of the powder, and when used in cosmetics, they improve the “feel” of the product.
The reagents and methods used to treat the powder surface are chosen taking account of properties regarding the nature of the powder surface to be treated and the dispersing medium. For example, there is lipophilic treatment by oils or metal soaps, hydrophilic treatment by surfactants or water-soluble polymers, or water-repellent/oil-repellent treatment by silicone oils.
Among these, silicone compounds which have excellent feel, water repellent properties and stability are becoming increasingly widely used as oils. In order to improve the miscibility of the powder, a surface treatment using methyl hydrogen siloxane has been proposed in Japanese Patent No. 02719303 (Koho), and a surface improvement by a straight chain, single-terminated alkoxy-modified silicone has been proposed in Japanese Patent Application Public Disclosure (Kokai) Hei 7-196946 (Koho). Further, to improve dispersibility in the silicone oil, Japanese Patent Application Public Disclosure (Kokai) Hei 10-167946 (Koho) discloses a method wherein a polyether-modified silicone with a HLB of 2-7 is used as a dispersant.
However, although aggregation and sedimentation were improved in these surface-treated powders, further improvements were still desired. Depending on the treatment agent or treatment method, the powder and treatment agent tended to separate from the cosmetic material, or the powder became lumpy with passage of time and was difficult to re-disperse, so product quality and feel were adversely affected. It was therefore desired to develop a powder composition and powder dispersion with little cohesion, excellent dispersibility and time-dependent stability, and a pleasant feel.
It is therefore a first object of this invention to provide a powder composition having little cohesion and excellent dispersibility.
It is a second object of this invention to provide an oil-based powder having little cohesion and excellent time-dependent stability.
It is a third object of this invention to provide a cosmetic material having excellent usability and good time-dependent stability.